Method of temperature control



July 28, 1942. R. 1.. FEARN O METHOD OF TEMPERATURE CONTROL Filed May 24, 1940 Patented July 28, 1942 i 3 METHOD OF TEMPERATURE CONTROL Richard L. Fearn, Rockville, Md., assignor to The Drever Company, Philadelphia, Pa., a corporation of Pennsylvania Application May 24, 1940, Serial No. 337,056

Claims.

A principal object of this invention is to provide an improved method of controlling temperature in processes involving the heating of metals.

Another and more particular object is to provide an improved method of accurately regulating the degree of heat treatment taking place in a strand of metal passing continuously through a zone of elevated temperature.

It is known that for each metal and alloy there is a definite tensile strength for each temperature, and tensile strength, therefor, may be used as a measure of temperature. A like relationship exists between yield strength and temperature, and this phenomenon is employed in the device hereinafter described.

In accordance with my invention, a metal strand, while passing through a heated zone, as in a strand-heating machine, is subjected to a stretch load of predetermined definite magnitude. When the temperature of the wire reaches the point where the yield strength becomes less than the load, the strand will elongate, and if some means is provided whereby this elongation may be observed, and since the magnitude of the said load is known, there is afforded an accurate indication of the temperature to which the strand has been elevated in moving through the heated zone at the prevailing rate of speed. By adjusting the load to a magnitude which will correspond to the yield strength of the strand at the temperature at which the heat treatment is to be conducted; by then correlating the heating zone and the speed of the strand so that the latter in passing through the zone will be elevated to said temperature as indicated by the yielding of the strand; and by subsequently re-correlating the heating Zone and the speed, as may be required, so as-to maintain continuously a constant rate of elongation in the moving strand, it is possible to effect a substantially uniform and highly accurate heat treatment of the entire strand. In the preferred embodiment of my invention, the aforesaid correlations are effected automatically in accordance with the changes in length occurring in that portion of the strand which is at any moment traversing the heating zone.

In the attached drawing:

Figures 1 and 2 are diagrammatic views showing two heat-treating machines incorporating the principle of my invention, and

Fig. 3 is a detached view of one of the elements of the machine illustrated in Fig. 1.

The machine illustrated in Fig. 1 comprises essentially a heater I, of the flame-type for example, a payoff reel 2 from which the wire or other heat-treated wire.

strand is withdrawn for passage through the heater, and a takeup reel 3 which receives the In the present instance a quenching or cooling chamber 4 is provided to and through which the strand passes from the heater I. Between the payoff reel 2 and .the heater is a sheave 5 over which the strand passes, and this sheave is mounted on a movable support consisting in the present instance of a bracket 6 which is pivotally supported at I on the fixed structure of the machine. An arm 8 extends transversely from the bracket 6, and this arm carries a weight 9 which tends to turn the bracket 6 around the pivot I so as to draw the sheave 5 away from the reels 2 and 3. Intermediate the reel 2 and the sheave 5 is a capstan I9 around which the Wire passes in well known manner, and a second capstan I I is located between the end of the heater I and the takeup reel 3. In the present instance, the capstans I0 and I I are driven at the same rate of speed, but the capstan I I is somewhat larger in diameter than the capstan Ii). It is apparent that the wire in passing from the one capstan to the other is placed continuously under a tension load the magnitude of which is determined by the weight 9. Any variation in length in the portion of the wire extending between the capstans results necessarily in a movement of the bracket 6. In the present instance, the capstans II] and II are shown as operated from a motor I2. It will be noted by reference to Fig. 3 that instead of two individual capstans, a single capstan I3 may be used having conjoined sections of the required difierent diameters.

In the present instance, the heater I is of the flame type well known in the art, and comprises a plurality of separate burners arranged in series longitudinally of the heater, over which burners the wire passes in transit through the heater. The respective burners are fed with fuel through individual ducts, I4, I5, I6, IT, IS and I9, respectively, and all of these ducts are controlled through the medium of a valve 20 which is constructed and arranged so that in one direction of movement, to the right as viewed in the drawing, the ducts I4 to I9, inclusive, will be connected successively in the order named with the source of fuel (not shown). The valve is such that each individual duct, when connected with the said source of fuel, will remain connected until the movement of the valve is reversed. Movement of the valve to the left will in the reverse order disconnect the ducts, I9 to I4, inclusive, from the source of fuel supply. The specific details of the valve form no part of the present invention. It

will be noted that other types of heater may be used in lieu of that described above, such for example as a tube heater, together with any suitable form of throttling valve or other means for controlling the effective temperature in the heater.

The movable element of the valve is connected mechanically through a connecting rod 2| with the lower end of the bracket 6 at a point below the pivot I, so that any movement of the upper or sheave-supporting end of the bracket to the left will tend to connect the burners consecutively from left to right with the source of fuel, and movement of the upper end of the bracket to the right will have the reverse eiiect of consecutively disconnecting the burners from said source.

In the operation of this device, the weight 9 is regulated to aiTord a tension load on that portion of the Wire extending between the sheave and the capstan l I, which portion traverses the heater l, of a magnitude which will cause the wire to initially yield at the desired temperature for the. heat treatment. When the machine is set in operation, there will be a tendency, by reason of the slightly greater diameter of the capstan ll over that of the capstan It], to draw the sheave to the left, but this is immediately corrected when the wire as it passes through the heater is ele'-' vated to the yield strength temperature at the predetermined tension load. The initial movement of the sheave to the left will tend to increase the efiective temperature in the burner by connecting additional burners with the source of fuel, so that the heating rate is increased, and the subsequent movement of the sheave to the right will have the opposite effect of decreasing the heat applied to the wire. The device, there fore, will automatically regulate itself to maintain the heating conditions in the heater at the point where the wire in passing through will be heated to the desired heat-treating temperature. Since the sheave I I, by reason of its larger diameter tends continually to take up the extra length developing in the wire as a result of its'yield at the given temperature, a substantial balance is obtained, wherein the sheave 5 remains substantially in one position, and any variations in the effective length of the wire due to underor overheating will be automatically corrected by the corresponding movement of the sheave and the resulting actuation of the valve 20 as described above.

It is apparent that the adjustment of the valve to maintain the desired temperature in the wire may be effected manually in accordance with the index afiorded by movements of the sheave 5, and if this manual adjustment is desired, the lower end of the bracket 6 may be associated with a suitable dial 22 which will indicate the movements of the sheave in either direction from a normal position. It will be apparent, also, that theoretically the temperature to which the wire is elevated in transit through the heater may be regulated by adjustments in the rate of movement of the wire. The efiective temperature in the heating zone in relation to the Wire, in other words, is a function of the rate of speed of the wire as well as the actual temperature in the heater to which the wire is subjected, and may be regulated by adjustments either of the rate of speed or of the said actual temperature, or both. I have found it desirable, however, to em ploy a heating means which is quick acting and capable of bringing the wire rapidly to the desired temperature, to move the wire through the heater at a corresponding high rate of speed,

and. to regulate the effective temperature by adjustments of the heater alone. This has the effect not only of maintaining production at a maximum but also reduces lag in the operation of the control means to a minimum and maintains the temperature substantially constant.

From the foregoing description, it will be apparent that the degree of elongation of the wire at the given temperature will be substantially constant throughout the entire length of the wire passed through the machine. The actual degree of stretch occurring in the wire at the yield temperature is determined in the present instance by the difierence in the diameters of the capstans l0 and Ii. While the degree of .stretch is not critical, I have found that a stretch of 1%, i. e., that afiording a total elongation in the treated length of wire of 1%, is highly satisfactory. This degree of stretch gives a negligible elongation and at the same time affords adequate sensitivity in the control device.

A'modification of the device. is illustrated diagrammatically in Fig. 2 of the drawing. In this case, the wire passing from the payroll reel 23 to the takeup reel 24 passes through a heater 25, and at each side of the heater around a capstan, designated respectively by the reference numerals 26 and 21. The capstans in this instance are of the same diameter and are driven from a motor 28, the rotational speed of the capstan 2! being slightly greater than that of the capstan 2 6 so'as to impose a tension on the intervening length of wire. The capstan 21 is movably mounted and is restrained from movement to the left, as viewed in the drawing, by a calibrated spring 29. The outer end of the spring is anchored to a member 30 which is adjustably supported in the fixed structure of the machine and which is provided with means for releasably securing it in adjusted position to said structure. By adjusting the member 30 to the left or right as viewed in the drawing, the tension of the spring may be decreased or increased as required. The driving connection between the motor 28 and the capstan Z1 is a flexible one to permit movements of the capstan toward and away from the capstan 26. Movements of the capstan 21 are indicated upon a dial 31 While not shown in the drawing, it is apparent that the capstan 21 may be operatively connected with a suitable means for regulating the efiective temperature in the heater 24, such, for example, as the throttling device previously described, in connection with the embodiment of the invention shown in Fig. 1.

It will be apparent also that other than a stretching force might be applied to th metal in order to, obtain the characteristic distortion at the yield temperature which constitutes the basis for temperature control in accordance with the invention. A bending force might be employed, for example; and. in certain applications a force of compression. Th term tension, therefore, is herein employed. in the liberal sense, and is not necessarily restrictive, as to the character of distortion occurring under the given circumstances at the yield temperature It will be noted further that the term strand as herein used is intended to embrace any character of metal form in addition to wire, such for example as ribbons, rods, tubes, sh ets, bars, etc., which is capable of continuous handling in accordance wi thepr ced r et for h- When he, m ch e. is e ope t n, the

slightly greater speed of the capstan 21 over the capstan 26 will tend to draw the capstan 26 to the left as viewed in the drawing, and this tendency is resisted by the spring 29. The actual tension load imposed upon the portion of the wire extending between the two capstans may be regulated by adjustment of the member 29, and the tension load will be adjusted to correspond with the yield strength of the strand at the particular desired heat-treatment temperature. With an operative connection between the heater and the capstan 21 such as described above, the device will operate automatically to maintain a constant heat-treatin temperature; and it is apparent that the temperature control may also be effected manually in accordance with the index afforded by the dial 3 I.

I claim:

1. The method which consists in subjecting a metal strand to a constant stress corresponding to the yield strength of the strand at a given temperature, progressively locally heating the strand to the point where yield occurs, and regulating the effective heating temperature as required to maintain the rate of yield substantially constant.

2. The method which consists in passing a metal strand continuously through a zone of elevated temperature, maintaining the strand in transit through said zone under a constant deformation load calculated to cause the heated metal to yield at a given temperature, and regulating the effective heating temperature so as to maintain continuously a substantially uniform rate of deformation in the strand.

3. The method of heating metal strands, which consists in passing a strand continuously through a zone of elevated temperature, maintaining the strand in transit through the zone under a constant tension stress corresponding to the yield strength of th strand at a given temperature, regulating the said effective heating temperature of said zone so as to bring the strand in transit to said given temperature as indicated by elongation of the strand, and thereafter continuing to regulate the said effective temperature as required to maintain the rate of said elongation substantially constant,

4. The method which consists in passing a metal strand continuously while under a constant stress corresponding to the yield strength of the strand at a given temperature through a heating zone wherein said strand is heated to the point where yield occurs, and regulating the effective temperature of said zone in accordance with variations in the rate of the elongation of the strand resulting from said yield 50 as to maintain said rate substantially constant.

5. In the heating of metal strands by continuous passage thereof through a zone of elevated temperature, the method of temperature control which comprises as steps thereof subjecting the strand continuously to a constant stress corresponding to the yield strength of the strand at the desired heating temperature, and regulating the effective temperature of said zone, first to bring the strand to said desired temperature, and thereafter to maintain the rate of the resulting elongation of the strand substantially constant.

RICHARD L. FEARN. 

